Quantity and Configuration of Available ElephantHabitat and Related Conservation Concerns in the LowerKinabatangan Floodplain of Sabah, MalaysiaJason G. Estes1,2*, Nurzhafarina Othman3,4, Sulaiman Ismail5, Marc Ancrenaz5,6,7, Benoit Goossens3,4,6,

Laurentius N. Ambu6, Anna B. Estes8, Peter A. Palmiotto1

1 Department of Environmental Studies, Antioch University New England, Keene, New Hampshire, United States of America, 2 Department of Environmental

Conservation, University of Massachusetts, Amherst, Massachusetts, United States of America, 3 Organisms and Environment Division, School of Biosciences, Cardiff

University, Cardiff, United Kingdom, 4 Danau Girang Field Centre, Sabah Wildlife Department, Kota Kinabalu, Sabah, Malaysia, 5 Hutan, Kinabatangan Orang-utan

Conservation Program, Kota Kinabalu, Sabah, Malaysia, 6 Sabah Wildlife Department, Kota Kinabalu, Sabah, Malaysia, 7 North of England Zoological Society, Honorary

Conservation Fellow, Chester, United Kingdom, 8 Center for Regional Environmental Studies, Dept. of Environmental Sciences, University of Virginia, Charlottesville, North

Carolina, United States of America

Abstract

The approximately 300 (298, 95% CI: 152–581) elephants in the Lower Kinabatangan Managed Elephant Range in Sabah,Malaysian Borneo are a priority sub-population for Borneo’s total elephant population (2,040, 95% CI: 1,184–3,652). Habitatloss and human-elephant conflict are recognized as the major threats to Bornean elephant survival. In the Kinabatanganregion, human settlements and agricultural development for oil palm drive an intense fragmentation process. Electricfences guard against elephant crop raiding but also remove access to suitable habitat patches. We conducted expertopinion-based least-cost analyses, to model the quantity and configuration of available suitable elephant habitat in theLower Kinabatangan, and called this the Elephant Habitat Linkage. At 184 km2, our estimate of available habitat is 54%smaller than the estimate used in the State’s Elephant Action Plan for the Lower Kinabatangan Managed Elephant Range(400 km2). During high flood levels, available habitat is reduced to only 61 km2. As a consequence, short-term elephantdensities are likely to surge during floods to 4.83 km22 (95% CI: 2.46–9.41), among the highest estimated for forest-dwellingelephants in Asia or Africa. During severe floods, the configuration of remaining elephant habitat and the surge in elephantdensity may put two villages at elevated risk of human-elephant conflict. Lower Kinabatangan elephants are vulnerable tothe natural disturbance regime of the river due to their limited dispersal options. Twenty bottlenecks less than one km widethroughout the Elephant Habitat Linkage, have the potential to further reduce access to suitable habitat. Rebuildinglandscape connectivity to isolated habitat patches and to the North Kinabatangan Managed Elephant Range (less than35 km inland) are conservation priorities that would increase the quantity of available habitat, and may work as amechanism to allow population release, lower elephant density, reduce human-elephant conflict, and enable geneticmixing.

Citation: Estes JG, Othman N, Ismail S, Ancrenaz M, Goossens B, et al. (2012) Quantity and Configuration of Available Elephant Habitat and Related ConservationConcerns in the Lower Kinabatangan Floodplain of Sabah, Malaysia. PLoS ONE 7(10): e44601. doi:10.1371/journal.pone.0044601

Editor: Andrew Hector, University of Zurich, Switzerland

Received May 20, 2011; Accepted August 9, 2012; Published October 5, 2012

Copyright: � 2012 Estes et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permitsunrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Funding: The authors greatly appreciate our funders including the Center for Tropical Ecology and Conservation (CTEC), Idea Wild, the Rainforest InformationCenter (RIC), The Mohamed Bin Zayed Species Conservation Fund, ARCUS Foundation, Abraham Foundation, Shining Hope, Foundation Ensemble, Cared for theEarth, World Women Work, World Land Trust, Wildlife Conservation Network, Elephant Family, AOP, the U.S. Fish and Wildlife Service, and the following zoos:Columbus, Houston, Pittsburgh, Cleveland, Oregon, Philadelphia, Woodland Park, Phoenix, Basel, Bush Gardens, Boise, Hogle, Chester, Apenheul, La Palmyre,Beauval, Saint-Louis, Victoria, and Roger Williams Park. Our generous funders had no role in study design, data collection and analysis, decision to publish, orpreparation of the manuscript.

Competing Interests: The authors have declared that no competing interests exist.

* E-mail: jasongestes@gmail.com

Introduction

As wildlife habitats and populations become increasingly

isolated, assessing the relative potential for animal movement

between habitat patches, known as the permeability of the

landscape [1], becomes increasingly important to understanding

a landscape’s functional connectivity. Landscape permeability is

species specific, is linked to both habitat composition and

configuration in a landscape, and is spatially and temporally

complex. Spatially, managers must consider movement of target

species at multiple scales. Landscape connectivity that supports

intra-territorial movement necessary for wildlife to access habitat

resources may not maintain movement at greater spatial scales

such as the inter-territorial movements influencing metapopula-

tion function, dispersal, and range shifts [1]. Temporal consider-

ations are also necessary as natural disturbances can temporarily

reduce permeability [1]. A lack of connectivity can leave otherwise

suitable wildlife habitat unoccupied [2] resulting in discrepancies

between the spatial distribution of suitable habitat and species

occupancy [3].

Limiting elephant (Elephantidae) movement options and reducing

habitat area available to them have a myriad of cascading

consequences. The disruption of natural movements of elephants

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due to human actions such as fencing, habitat reduction,

fragmentation, and transformation is a cause of locally high

elephant densities [4]. High elephant densities have been cited for

degradation to vegetation [5] and subsequent negative effects on

other species [6]. Limited connectivity in a landscape can also

leave populations vulnerable by removing their ability to shift their

range in response to natural landscape processes and the effects of

climate change [7]. Reduction of land available to elephants can

both elevate elephant densities in remaining habitat patches and

increase the human-elephant interface; two phenomenon that

have been linked to increased levels of crop raiding [8–10].

In the early 1980s, Borneo’s elephants (Elephas maximus borneensis)

in Sabah, Malaysia were estimated to number between 500 and

2,000 [11]. The estimate was updated in 2002 to approximately

1,100 to 1,600 individuals with methods primarily based on

habitat availability [12]. Recent work based on distance sampling

of dung piles, estimated the total population of Bornean elephants

(mostly in Sabah) at around 2,000 (published estimate: 2,040, 95%

CI: 1,184–3,652), all residing in the northeastern portion of the

island [13].

The Sabah Wildlife Department declared four Managed

Elephant Ranges: the Lower Kinabatangan (400 km2), North

Kinabatangan (1,400 km2), Tabin (1,200 km2), and Central Sabah

(7,900 km2), which hold over 90% of Sabah’s wild elephant

population in its current Elephant Action Plan (Fig. 1) [12,14].

These ranges were based upon the current and likely future

pattern and extent of forested land in the state as well as the

number of elephants residing within the Ranges [12]. The Lower

Kinabatangan Managed Elephant Range population is estimated

at about 300 (published estimate: 298, 95% CI: 152–581)

elephants [13], living within a matrix of protected and unprotected

lands. Although estimates for conducting population surveys were

very different, managers believe there has been a twofold increase

in the ten years since the late nineties when the population was

estimated at 95–115 elephants [14]. In 2005, the Lower

Kinabatangan Wildlife Sanctuary successfully secured protection

for 260 km2 of forest and connected approximately 150 km2 of

Virgin Jungle Reserves already protected within the Lower

Kinabatangan (Fig. 2). This conservation effort protects a semi-

continuous corridor of natural vegetation connecting the coastal

mangrove swamps with dry forests upriver in the central parts of

the state. However, the overall reduction in available habitat, the

disruption of elephant migration routes, and the subsequent

intensification of human-elephant conflicts are all cited as

conservation threats in the Lower Kinabatangan Managed

Elephant Range [14].

Habitat loss is a major obstacle for elephant conservation

statewide in Sabah and particularly in the Lower Kinabatangan.

Habitat loss in the Lower Kinabatangan occurs directly through

conversion of existing forests to other land-use such as agriculture

or human settlement, while habitat isolation results from related

fragmentation processes. Sabah lost approximately 40% of its

forests in the 20th century [15]. Over five years (1998–2003),

2,926 km2 of oil palm (Elaeis guineensis) plantation was created in

Sabah, representing an average annual growth rate of 6.1% [16].

Oil palm in the Lower Kinabatangan accounts for about 28% of

the total oil palm area in Sabah [17]. Plantations reduce the

quantity of habitat available to elephants and are a source of

conflict when elephants graze on oil palm trees. An estimated 80%

of the Lower Kinabatangan floodplain has today been converted

to agriculture or other human-made, non-forest land cover.

Conversion of forest to agricultural land in the Lower Kinaba-

tangan has fragmented elephant habitat and elephant populations

[12]. The conversion process in the Kinabatangan is also credited

with creating conflicts between elephants and people by disrupting

traditional elephant migration routes, and increasing the risk of

crop predation, damage to property, damage to local cemeteries,

and loss of human life [12].

We suspected that available elephant habitat was overestimated

by elephant management plans for the region, so we sought to

identify the current quantity and configuration of available

suitable habitat in the Lower Kinabatangan Managed Elephant

Range. By comparing our habitat estimates with previous

estimates of available habitat, we aimed to demonstrate the

importance of incorporating both landscape permeability and the

natural disturbance regime into elephant habitat estimates for this

area. Another objective was to compare elephant density among

the different habitat quantity estimates using the most recent

Kinabatangan elephant population numbers available. To aid in

management of this landscape we also conducted an analysis of

bottlenecks in the Lower Kinabatangan. Lastly, we included

discussion of what our estimates may suggest about human-

elephant conflicts in the region.

Materials and Methods

Study areaResearch was conducted in the Lower Kinabatangan floodplain

of Sabah, Malaysia (approximate range of the study area is 5u189N

to 5u429N and 117u549E to 118u339E). The Kinabatangan River is

560 km long, has a water catchment area of about 16,800 km2,

and is subject to the Northeasterly Monsoonal climate. The mean

annual rainfall is about 3,000 mm with the heaviest precipitation

from October to March [18]. The region’s matrix of habitat types

include riparian forest, seasonally flooded forest, swamp forest, dry

dipterocarp forest, estuary nipa palm (Nypa fruticans), and

mangrove.

This study focused on the area between the villages of Abai and

Batu Puteh (Fig. 2). Beyond Abai, elephants are restricted by vast

mangrove forest. Beyond Batu Puteh, elephants are blocked from

traveling upriver by a major road bordered by human settlement.

The study area contains lots 1–7 (approximately 218 km2) of the

Lower Kinabatangan Wildlife Sanctuary (LKWS) and approxi-

mately 89 km2 (calculation does not include mangrove forest

reserves) of protected forest reserves (Fig. 2). The disturbance

regime of the Lower Kinabatangan is characterized by seasonal

flooding and occasional severe floods, which inundate the study

area. The highest recorded flood level as of 2001 was 14 m above

sea level [18]. Severe floods also occurred in 1971, 1974, 1977,

1981, 1986, 1996, and 2000. In 2000, WWF Malaysia estimated

that 100 km2 of the Lower Kinabatangan was inundated with

water for approximately 22 days. Negative effects were reported

on elephants when approximately 80% of the Lower Kinabatan-

gan Wildlife Sanctuary was flooded [18]. During the floods of

1996, inundation lasted for 35 days from the village of Sukau,

about 140 km upriver, to the village of Kuala Karamuak (Fig. 1)

[18]. The most recent major flood occurred in 2010.

Available elephant habitat modelingLandscape suitability and permeability for elephants was

modeled through least-cost analysis facilitated by CorridorDe-

signer [19], a suite of GIS tools created for Arc GIS [20]. Four

GIS layers (factors), representing land cover, linear barriers,

swamps, and level of protection, were created from a combination

of satellite images, scanned paper maps, field data, and local

knowledge (Text S1).

A team of eight experts, all with extensive experience observing

the Kinabatangan elephants, provided the weighting of the

Available Elephant Habitat in the Kinabatangan

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‘‘expert opinion-based model’’ (Table S1). The team consisted of

one professional researcher who had worked in the Kinabatangan

over a decade, two graduate students studying the Kinabatangan

elephants, and five local field research assistants who were

employed full-time to track and study this population of elephants.

The team of experts weighted each of the four factors and the suite

of classes within them. Both factors and classes were given weights

between 0 and 100. However, the sum of all factor scores for each

expert had to sum to 100 in order to account for the relative

importance of each factor. Class scores were allowed to vary

independently within the weighting range.

Weighting of factors and classes occurred during an in person

meeting to allow participants to ask clarifying questions through-

out the process. Participants assigned weights without knowledge

of other participants’ weights. The experts based their opinions on

their field observations of the Kinabatangan’s elephants and the

current body of knowledge about Bornean elephants and elephant

populations elsewhere. Each participant score was given equal

weight with opinions averaged for use in the ‘‘expert opinion-

based model.’’

In the land cover factor, the expert opinion-based model

assigned high suitability to regenerating forest, also known as

logged over forests, since these areas are believed to hold the

highest proportion of forage for elephants. Riparian habitat along

the Lower Kinabatangan River, often characterized with sandy

substrate and open grassy areas, was also rated with high

suitability. Human settlements were given a low suitability score

since people tend to push elephants out of these areas. Similarly,

oil palm plantations, although holding a great deal of forage for

elephants, were rated low due to the fact that people generally

protect them from elephants. Electric fences and trenches in the

linear barriers factor layer, and the three swamp classifications in

the swamps layer, were given low suitability scores since these have

been observed to inhibit elephant passage. CorridorDesigner

operates under the assumption that habitat suitability is synony-

mous with permeability while landscape resistance is defined as the

inverse of suitability.

Factor and class weights were used to create the expert opinion-

based Habitat Suitability Model (HSM). The four factors were

combined with a geometric mean algorithm to reflect that one

factor, such as linear barriers in the Lower Kinabatangan, can

limit suitability of the pixel in a way that cannot be compensated

by other factors [19]. Since an important aspect of least-cost

analyses is Euclidean distance, two artificial habitat patches were

placed as endpoints behind the known upriver and downriver

extents of the Kinabatangan elephants’ range. This was done to

Figure 1. Managed Elephant Ranges of Sabah, Malaysia.doi:10.1371/journal.pone.0044601.g001

Available Elephant Habitat in the Kinabatangan

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give the models ‘‘room to run,’’ so that the modeled corridor

would not simply represent the shortest distance between the

starting and ending habitat patches [19]. Providing source and

destination points allowed us to take our point specific HSM (cost

surface), and address route specific connectivity [21] with a cost-

distance surface. The cost-distance surface combines cost of travel

for an elephant with distance. This cost-distance grid was then

used to generate a least-cost corridor model, illustrating the two

dimensional configuration of the most permeable pathway

between the two endpoints.

In addition to the expert opinion-based model, 21 other HSMs,

cost-distance grids, and least-cost corridors were created using

biologically plausible alternatives with input weights ranging

within plausible bounds (Table S1). Varying the weights of model

inputs provided variation in outputs. One assumption is that the

modeler is able to produce much of the variation in model outputs

that could be attained from various combinations of model weights

falling within reasonable bounds. These alternative models were

used to conduct uncertainty analysis on the final linkage design

(the Lower Kinabatangan Elephant Habitat Linkage) of available

suitable elephant habitat.

The expert opinion-based model and one alternative model,

which identified a different pathway around the village of Sukau,

were merged in order to capture the majority of variation among

all models. This output was considered the most permeable

suitable portion of the landscape if an elephant was traveling

between the two endpoints and was referred to as the least-cost

corridor.

The Elephant Habitat Linkage, representing all available

suitable habitat for elephants in the Lower Kinabatangan

floodplain, was created by merging the least-cost corridor with

all intersecting habitat patches. Elephant habitat patches (Fig. 3)

for the entire study area were determined using CorridorDesigner

tools, with a 50 m moving window, a minimum patch size of

1000 m2, and the expert opinion-based HSM.

Uncertainty analysisUncertainty analysis was conducted to assess how susceptible

the least-cost corridor and the Elephant Habitat Linkage were to

variations in model weighting and design. Uncertainty analysis

addresses how much the model output varies in response to

uncertainty in the input parameters. The model can be considered

robust to uncertainty, if the range of assumptions is wide enough to

be credible and the subsequent inferences are narrow enough to be

useful [22,23]. To calculate the amount of variation captured by

the least-cost corridor and the Elephant Habitat Linkage, the

proportion of area of each of the 21 alternative models contained

within the least-cost corridor and the Elephant Habitat Linkage

was calculated [22].

Both the least-cost corridor and the Elephant Habitat Linkage

were robust to uncertainty in input parameters (Fig. S1). The

minimum proportion of any alternative model captured by the

area of either the least-cost corridor or the Elephant Habitat

Linkage was 92.5%. The least-cost corridor captured an average

of 97.5% of the 20 alternative models, while the Elephant Habitat

Linkage captured an average of 99.3% of all alternatives.

Figure 2. Map of the Lower Kinabatangan study area with protected forest reserves and the Lower Kinabatangan WildlifeSanctuary.doi:10.1371/journal.pone.0044601.g002

Available Elephant Habitat in the Kinabatangan

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Although almost all variation among the models was captured by

the Elephant Habitat Linkage, we do acknowledge that much of

the Elephant Habitat Linkage is hemmed in by fenced oil palm

plantations, which can explain some of this lack of sensitivity in

model weighting [22]. Other modeled corridors including Beier et

al. (2009), Schadt et al. (2002), and Larkin et al. (2004) also

reported robustness to uncertainty in model inputs [22,24,25].

Habitat quantity and elephant density analysisFour different area calculation methods of available habitat for

elephants in the Lower Kinabatangan for elephants were

compared to examine the differences in habitat quantity. The

first area calculation was taken from Sabah’s most recent Elephant

Action Plan which represented the Lower Kinabatangan Managed

Elephant Range as 400 km2 [14]. The second area calculation,

termed visually contiguous forest, consisted of all forested and

riparian area, excluding mangrove forests, which would appear

contiguous if looking at aerial images. The Elephant Habitat

Linkage provided the third available habitat area calculation,

representing both functional connectivity and habitat suitability

specific to the Lower Kinabatangan’s elephants. The fourth area

calculation was the Elephant Habitat Linkage area minus all areas

inundated with water during severe floods. The flood zone map

layer was based on map created by WWF Malaysia using aerial

photos of flood levels recorded in 1996 (Text S1). The area of the

flood zone within the study area was calculated after digitizing the

flood zone. The full area of the remaining Elephant Habitat

Linkage was calculated including the area of each habitat

fragment over 0.005 km2. The ratio of flood zone total area and

Elephant Habitat Linkage area was calculated to compare the size

difference between natural flooding disturbance and available

suitable elephant habitat.

Elephant density was calculated for each of the available habitat

area estimates by dividing the area of available habitat by the

number of elephants in the Lower Kinabatangan. Since estimating

elephant numbers was beyond the scope of this study, elephant

density in the Kinabatangan was based on a recently conducted

population survey (298, 95% CI: 152–581) based on distance

sampling of dung piles [13]. We also used this estimate since it is

the estimate used in Sabah’s Elephant Action plan for 2012–2016

[14].

Bottleneck analysisBottlenecks were defined as any portion of the Elephant Habitat

Linkage centerline where the width was less than one km. This

width was chosen to be consistent with successful elephant corridor

width thresholds elsewhere in Asia [26]. The length that each

bottleneck remained below the threshold was calculated. Each

bottleneck was put into one of three categories depending on

whether human-created or natural landscape features caused the

bottleneck. Human features included landscape elements such as

fences, human settlement, and agriculture. Natural landscape

features included elements such as oxbow lakes, limestone

outcroppings, and large swamps. Categories for identifying

Figure 3. Map of the Elephant Habitat Linkage and isolated suitable elephant habitat patches.doi:10.1371/journal.pone.0044601.g003

Available Elephant Habitat in the Kinabatangan

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bottleneck cause included: human/human, where the bottleneck

was bordered by human features on each side of the centerline,

natural/natural, where natural landscape features were on each

side of the centerline, and human/natural, where a combination of

human and natural features caused the bottleneck.

Results

Modeled available elephant habitat: quantity andconfiguration

The Elephant Habitat Linkage (Fig. 3) covers an area of

approximately 184 km2 and is our estimate of the current quantity

and configuration of available suitable elephant habitat in the

Lower Kinabatangan Managed Elephant Range. It passes close to

the villages of Abai, Sukau, Bilit, and Batu Puteh. As a thin strip

following the Kinabatangan River, the Elephant Habitat Linkage

has an average width of only 1.3 km. At its widest, the Linkage

spans 3.3 km, while the narrowest portion is 0.1 km. The widest

portions include Lower Kinabatangan Wildlife Sanctuary lots 2, 6,

and the combination of lots 3 and 4.

The area with visual connectivity of forests in the Lower

Kinabatangan was estimated at 351 km2. This area is 12% smaller

than the most recent documented area of the Lower Kinaba-

tangan Managed Elephant Range. The Elephant Habitat Linkage,

at 184 km2, is a reduction in area of 54% from the published

Lower Kinabatangan Managed Elephant Range and 47% from

our visual connectivity estimate.

During times of extensive flooding (as seen in 1996), approx-

imately 423 km2 of the study area is inundated with water and

more than 120 km2 of the Elephant Habitat Linkage is flooded,

reducing the area available to elephants within the Elephant

Habitat Linkage by 66% (62 km2 Elephant Habitat Linkage

remaining). Inundation for much of this area lasted for 35 days

[18]. Floodwaters break the Elephant Habitat Linkage into 23

fragments over 0.005 km2 that range in size from 31 km2 to

0.007 km2 (mean = 2.68 km2, SD66.67 km2), representing a total

area (62 km2) that is only 15% of the size of the Lower

Kinabatangan Managed Elephant Range (Table 1).

Elephant densityElephant density varies dramatically based on the four area

calculations (Table 1). There was a 14% increase in elephant

density between the documented area of the Lower Kinabatangan

Managed Elephant Range and the visual connectivity approach. A

117% increase was found between the density of the Lower

Kinabatangan Managed Elephant Range area and the Elephant

Habitat Linkage. During flooding, the Elephant Habitat Linkage

will experience a surge in elephant density by 548% compared to

the Lower Kinabatangan Managed Elephant Range, and 198%

compared to the Elephant Habitat Linkage.

BottlenecksTwenty bottlenecks (,1.0 km width) were identified by our

model throughout the Elephant Habitat Linkage. Thirty-eight

percent of the Elephant Habitat Linkage’s centerline was below

the one km threshold. The average length for bottlenecks in the

Kinabatangan was 1.9 km (max: 9.0 km, min: 0.2 km, SD62.1).

The average length between bottlenecks was 3.2 km (max:

14.0 km, min: 0.3 km, SD64.2). Twelve bottlenecks, accounting

for 44% of total bottleneck length (17.2 km), were a result of both

human and natural features; four bottlenecks, representing 8% of

the total bottleneck length (3.1 km), were caused by only natural

features; and four bottlenecks, making up the remaining 48%

(18.6 km) of bottleneck length, were caused entirely by human

features.

Discussion

Available suitable elephant habitatRecent landscape change, such as extensive development of oil

palm plantations, has altered both the quantity and the

configuration of suitable habitat for elephants in the Kinabatangan

[18]. The Elephant Habitat Linkage provides a snapshot in time of

our estimate of both the quantity and location of available

elephant habitat in the Lower Kinabatangan.

The way in which managers classify available habitat clearly

affects the quantity of habitat assumed to exist. This study’s visual

connectivity area estimate (351 km2) is 12% smaller than the

documented area of the Lower Kinabatangan Managed Elephant

Range. The difference likely reflects variation in the definition of

available and suitable habitat but may also reflect landscape

change that has occurred since the declaration of Lower

Kinabatangan Managed Elephant Range. Inclusion of unreach-

able forest patches [27] (Goossens et al. unpublished data) west of the

major road at Batu Puteh also contributes to the discrepancy

between the Elephant Action Plan and Elephant Habitat Linkage

habitat estimates.

A visual connectivity approach likely provides a more accurate

estimate of available habitat compared to the Lower Kinabatan-

gan Managed Elephant Range estimate, however it is overly

simplistic. Within the Lower Kinabatangan’s contiguous natural

vegetation, both suitability and resistance vary due to a myriad of

landscape features. Limestone outcroppings, for example, cause

variation in permeability and suitability within visually connected

Lower Kinabatangan forests. Limestone outcroppings often have

steep slopes or cliff edges. Although these features can be small in

area, they create holes of unsuitable habitat within otherwise

suitable habitat and offer resistance in the landscape by acting as

barriers that elephants must circumvent. Elephants are capable of

navigating steep terrain when required, but have been document-

ed in Africa to avoid gradual slopes even when forage on these

slopes is optimal [28,29]. Our results demonstrate that without

Table 1. Habitat area and elephant density estimates.

Area Estimate Area (km2) Density (elephants km22)

Lower Kinabatangan Managed Elephant Range [12] 400.00 0.75 (95% CI: 0.38–1.45)

Visually contiguous forest 350.83 0.85 (95% CI: 0.45–1.66)

Elephant Habitat Linkage 184.23 1.62 (95% CI: 0.83–3.15)

Remaining Elephant Habitat Linkage during flooding 61.75 4.83 (95% CI: 2.46–9.41)

All density estimates were based on the population estimate of 298 (95% CI: 152–581) elephants [13].doi:10.1371/journal.pone.0044601.t001

Available Elephant Habitat in the Kinabatangan

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considering suitability and permeability, the amount of available

habitat for elephants may be greatly overestimated in the

Kinabatangan. Our estimation of current available suitable

elephant habitat (the Elephant Habitat Linkage) in the Lower

Kinabatangan, at 184 km2, is 54% smaller than the Lower

Kinabatangan Managed Elephant Range habitat estimate and

47% smaller than our visual connectivity estimate.

We took our available habitat area estimate one step further to

demonstrate the importance of including natural flooding distur-

bance in Lower Kinabatangan elephant habitat estimates. During

severe floods, the Elephant Habitat Linkage will be cut into 23

habitat fragments over the size of 0.005 km2 (Fig. 4) with a

combined area of approximately 62 km2 of non-contiguous

suitable habitat and an average fragment size of less than 3 km2.

Elephants may face the risk of being temporarily trapped within

these small habitat patches bordered by floodwaters, human

settlements, and fenced oil palm plantations. Severe floods render

66% of the Elephant Habitat Linkage temporarily unsuitable,

leaving a suitable area of only 15% the size of the Lower

Kinabatangan Managed Elephant Range.

Flooding in the Kinabatangan is an important natural

disturbance process that affects species, ecosystems, and landscape

structure. Management areas that maintain natural disturbance

regimes without the risk of negatively affecting species, ecosystems,

and landscape structure probably require areas several times larger

than the maximum disturbance size typical of the region [30]. The

Elephant Habitat Linkage falls far short of this, with the 1996

Lower Kinabatangan flood zone (423 km2) more than 2.3 times its

size. While we see value in managing currently unavailable habitat

patches in the Managed Elephant Range for the maintenance of

biodiversity and for the option to reconnect areas in the future, we

stress the importance of having a more realistic awareness of the

quantity of habitat available to elephants at any given time.

Elephant densityWhen relatively dense populations of elephants exist, whether a

result of natural population growth or growth by compression of

elephants into smaller areas, undesirable changes may occur to the

local habitat, vegetation, and other wildlife species [31–34].

Elephant density in the Kinabatangan (Table 1) surges during high

flood levels to levels among the highest estimated for forest

elephants anywhere in the world, comparing to 4 km22 in India

[35], and 3.18 km22 in the Central African Republic [36]. The

already high elephant density in the Kinabatangan may rise

quickly if additional habitat is lost or isolated, and if managers are

correct that the Lower Kinabatangan elephant population is

growing at a rate that produced a twofold increase since the late

1990s [14].

There is no density of elephants that can serve as a definition of

‘overabundance’ for all areas, and a prerequisite for taking any

action to manage elephant levels should include clear conservation

and management objectives [37]. Elephant induced degradation

of vegetation [5] which has negative effects on other species [6]

have fueled debate about elephant overabundance elsewhere but

has not yet been cited as a problem in the Kinabatangan.

However, there is a danger of mismanaging the Lower

Figure 4. Map of visually contiguous forest, the Elephant Habitat Linkage, and the 1996 flood zone.doi:10.1371/journal.pone.0044601.g004

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Kinabatangan elephant population when the quantity of habitat is

grossly overestimated in management plans.

Furthermore, provisional minimum home-range estimates for

Bornean elephants are between 250 km2 to 400 km2 in relatively

non-fragmented forests and 600 km2 in fragmented forests of the

Kinabatangan [27]. This suggests that the Elephant Habitat

Linkage may not be large enough to hold the full extent of an

elephant’s home range. Indeed, over 50% of GPS fixes from three

collared elephants in the Kinabatangan between July 2008 and

February 2009 were located in oil palm plantations (Goossens et al.

unpublished data), possibly suggesting that elephants access a

portion of their resources from behind electric fences. These

resources are unavailable when plantations are effectively fenced

or defended strongly by people and should be considered

unreliable to support the elephant population. Conservation

action is needed in the Lower Kinabatangan to increase available

habitat for elephants by providing functional connectivity to

existing habitat patches within the Kinabatangan (Fig. 3) and

outside of the Kinabatangan to other Managed Elephant Ranges

to the west.

BottlenecksThe configuration of elephant habitat in the Lower Kinaba-

tangan jeopardizes the ability for elephants to pass throughout the

Elephant Habitat Linkage. A total of 20 bottlenecks currently

squeeze elephants through habitat areas where the width is

narrower than 1 km. Eighty percent of all bottlenecks, and 92% of

total bottleneck length, are caused at least in part by human

landscape features such as oil palm plantations and human

settlement. The average length of these bottlenecks is almost two

km with the two longest bottlenecks (9.0 km and 6.5 km) serving

as the only options for elephants to pass by Sukau Village. If

elephants choose the pathway arcing farther outside Sukau

through lot 3 of the Lower Kinabatangan Wildlife Sanctuary,

then they would travel through more than nine km in a bottleneck

approximately 0.8 km wide (Fig. 5). If they chose to travel adjacent

to Sukau, they would be in a bottleneck area for about 6.5 km with

width varying from 0.5 to 0.6 km or less (Fig. 5). A study in India

investigated the length and width dimensions of corridors found to

be used by elephants. Both bulls and family groups used passages

0.5–1 km wide and less than about five km long. It was suggested

that bulls may use narrower passages, or ones with greater length

to width ratios, even if these corridor dimensions were unsuitable

for family groups [26]. The two bottleneck pathways around

Sukau both have greater length to width ratios than seen to be

effective in India, suggesting that some bottlenecks in the

Kinabatangan may be nearing critical thresholds for effective

use by elephants. Additionally, the average distance between

bottlenecks in the Lower Kinabatangan is just over three km,

which means elephants are frequently funneled into narrow

passages (Fig. 5).

Human-elephant conflict (HEC)A combination of the quantity and configuration of available

suitable habitat, high elephant densities, and bottleneck areas

make the Lower Kinabatangan susceptible to high levels of HEC

and put the villages of Bilit and Sukau particularly at risk.

Elephants passing by Sukau must travel within one of two long,

narrow bottlenecks. Bottlenecks act as funnels pinching the

pathway between larger habitat patches and may cause higher

incidences of conflict compared to areas outside of bottlenecks

[26].

Elephants may be discouraged from using the southern passage,

which takes them away from Sukau, due to its narrow northern

opening caused by a combination of electric fencing and limestone

outcroppings. Elephants choosing to pass closer to Sukau may

frequently encounter houses and subsistence crops of local people

on the south side of the Kinabatangan River.

High elephant densities resulting from population growth or

habitat reduction have been associated with increased levels of

HEC [8]. Additionally, the loss of elephant range [12], whether

through direct habitat conversion or inaccessibility caused by

isolation of habitat patches, increases the probability of contact

between elephants and people by increasing the human-elephant

interface [9] resulting in increased levels of crop raiding [10].

During severe floods, when the Kinabatangan experiences a surge

in elephant density, the two largest Elephant Habitat Linkage

fragments remaining dry are situated adjacent to the villages of

Bilit and Sukau. The majority of the Kinabatangan’s elephants

may be trapped in these areas until floodwaters recede. If this is

the case, the surge in elephant density and the proximity of the

largest remaining available habitat to Sukau and Bilit may

encourage HEC around these two villages.

Elephants will need to reach well-drained or higher ground

when the Kinabatangan floods, which will put them in direct

conflict with people. Oil palm plantation owners chose to plant on

the least flood prone land and actively rid the plantations of water

by digging trenches from their plantations to nearby rivers and

swamps, creating bunds along the river, and installing pumping

mechanisms. Elephants are left with land prone to flooding since

the majority of plantations owners have installed electric fences on

the plantation perimeter to exclude crop-raiding elephants. This

non-random landscape change, where the comparably flood-safe

land is chosen for plantations, puts elephants into conflict with

people when elephants take refuge in plantations to escape

floodwaters [18] and forage in areas currently planted with palm

oil while other foraging areas are temporarily unavailable.

DispersalElephant dispersal is clearly limited in the Kinabatangan by a

combination of electric fences, human settlements, and movement

resistant natural features with low permeability such as large

swamps. Gomantong Forest Reserve (Fig. 2), for example, is

isolated from the Elephant Habitat Linkage by a large swamp

which is bordered on each side by the electric fences of oil palm

plantations (Fig. 5). Large portions of Lower Kinabatangan

Wildlife Sanctuary lots 1 and 5 are modeled as unavailable due

to large swamps. Combinations of barriers limiting dispersal

abilities, puts the long term survival of elephants at risk by

reducing their capability to respond to natural flood cycles.

Unprotected lands between sanctuaries and reserves must

remain permeable in order for Lower Kinabatangan elephants

to travel the extent of their current range. Predictions have

doomed wildlife reserves to become islands of habitat sitting

among vast inhospitable human-modified landscapes [38,39].

However, if stakeholders in the Kinabatangan can increase the

permeability of the landscape between isolated habitat patches by

widening bottlenecks and establishing corridors, they may be able

to reduce levels of HEC, increase elephants’ abilities to respond to

the natural flooding regime, and allow for genetic mixing between

Sabah’s elephant populations.

Managers and their partners have already established the Lower

Kinabatangan Wildlife Sanctuary to provide some connectivity

among other protected forests. Modern approaches of responding

to overabundance of elephants in southern Africa, call for closed

populations to be ‘‘released,’’ resulting in the decompression of

populations and allowing natural processes rather than constant

human intervention, to limit the effects of overabundant elephant

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populations [4]. If Lower Kinabatangan managers can increase

available elephant habitat by reopening passages to other

Managed Elephant Ranges such as North Kinabatangan Man-

aged Elephant Range, managers may be able to avoid the

expensive management of overabundant populations. The Sega-

liud Lokan Forest Reserve (Fig. 1) section of the North

Kinabatangan Managed Elephant Range is less than 35 km

inland from the main road at Batu Puteh that severs connectivity

for elephants traveling westward. Sabah’s 2002 Action Plan

referred to the North Kinabatangan Managed Elephant Range

when it stated that prospects exist for a corridor to be created

which links the Lower Kinabatangan elephants with the extensive

forest blocks and elephant ranges farther inland [12]. The new

action plan (2012–2016) also mentions corridor creation between

the Lower and Northern Kinabatangan Ranges [14]. Conserva-

tion action creating this linkage is an important step for Sabah’s

elephants.

Opportunities and next stepsThe methods applied here can be used for elephant conserva-

tion throughout Sabah to reassess the quantity and configuration

of habitat actually available to elephants, identify areas where

natural and human made barriers are working in conjunction to

limit permeability or sever connectivity, locate suitable habitat

patches, and generate least-cost corridors and linkage designs to

identify permeable elephant movement routes with the goal of

reconnecting isolated elephant habitat and elephant populations.

Primary management goals should include: 1) increasing the

quantity of suitable habitat in the Kinabatangan by enhancing

landscape permeability and functional connectivity between the

Elephant Habitat Linkage and currently isolated suitable habitat

(Fig. 3), 2) widening both bottlenecks passing Sukau, and 3)

reconnecting the Lower Kinabatangan elephant population with

the elephants in Segaliud Lokan Forest Reserve to allow for

genetic mixing and decompression of the Lower Kinabatangan

elephant population.

Supporting Information

Table S1 Weights given to the expert opinion-basedmodel (model 1) and the 21 alternative models (models2–22).

( )

Figure S1 Percent of habitat area modeled by the expertopinion-based model (model 1) and all alternativemodels (models 2–22) that was captured by the ElephantHabitat Linkage area.

(DOCX)

Text S1 Information sources used to derive the fourfactor layers and flood map used in this study.

(DOCX)

Figure 5. Map of electric fences, bottleneck areas, and the Elephant Habitat Linkage.doi:10.1371/journal.pone.0044601.g005

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XLSX

Acknowledgments

This work in Sabah would not have been possible without the support of

the Economic Planning Unit (research pass number 2396) and the Sabah

Wildlife Department. We want to thank the Kinabatangan Orangutan

Conservation Project (KOCP) and their Elephant Conservation Unit

(ECU) for consistent help and expertise provided throughout the study. We

also greatly appreciate our funders including the Center for Tropical

Ecology and Conservation (CTEC), Idea Wild, the Rainforest Information

Center (RIC), The Mohamed Bin Zayed Species Conservation Fund,

ARCUS Foundation, Abraham Foundation, Shining Hope, Foundation

Ensemble, Cared for the Earth, World Women Work, World Land Trust,

Wildlife Conservation Network, Elephant Family, AOP, the U.S. Fish and

Wildlife Service, and the following zoos: Columbus, Houston, Pittsburgh,

Cleveland, Oregon, Philadelphia, Woodland Park, Phoenix, Basel, Bush

Gardens, Boise, Hogle, Chester, Apenheul, La Palmyre, Beauval, Saint-

Louis, Victoria, and Roger Williams Park.

Author Contributions

Conceived and designed the experiments: JGE PAP MA BG LA NO SI.

Performed the experiments: JGE SI NO MA BG. Analyzed the data: JGE.

Wrote the paper: JGE MA BG PAP ABE.

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